1. Field of the Invention
The present invention relates to a process for the chemical treatment of semiconductor wafers in the presence of HF and then in the presence of ozone, in particular for the cleaning of silicon semiconductor wafers.
2. The Prior Art
Processes for the wet chemical treatment of semiconductor wafers are already known. Regarding these processes, reference may, for example, be made to DE-A 19853486 and U.S. Pat. No. 5,662,743. The disclosure of these references relate to removing metallic contamination and particles from semiconductor wafers. This contamination generally interferes with the surface structure pattern.
The present invention relates to a process for the chemical treatment of semiconductor wafers, in which the semiconductor wafers are treated with a medium containing HF and then with a medium containing ozone, wherein the semiconductor wafers that are treated with the medium containing ozone are free of aqueous HF.
The medium containing HF which is used in the process according to the invention may be either pure hydrogen fluoride or an aqueous solution of hydrogen fluoride, i.e. hydrofluoric acid. In both cases the medium containing HF may be in the gas phase or in the liquid phase. The medium containing HF which is used according to the present invention is preferably an aqueous HF solution, particularly preferably one that contains HF in a concentration of from 0.001% to 10% by weight. The aqueous HF solution which is used according to the invention may also contain HCl in a concentration of from 0.001% to 10% by weight, preferably from 0.2% to 2.0% by weight. Apart from HF, optionally water and optionally HCl, the medium containing HF which is used according to the present invention preferably does not contain any other substances, for example surfactants.
Regarding the above mentioned HF concentration or HCl concentration, the percent by weight for the HF is based upon the total weight of the aqueous solution. The percent by weight for the HCl is based upon the total weight of the aqueous solution.
The medium containing ozone which is used in the process according to the invention may be either O3 gas or an aqueous O3 solution. The medium containing ozone which is used according to the invention is preferably an aqueous O3 solution, particularly preferably solutions that contain O3 in a concentration of from 1 to 50 ppm.
If aqueous HF solutions and/or aqueous ozone solutions are used in the process according to the present invention, it is preferable to employ solutions that have been prepared using deionized water.
In the process according to the present invention, the treatment with the medium containing ozone directly follows the treatment with the medium containing HF, without any additional step of washing with water. The omission of washing with water between the treatments with the chemically active agents offers immediate economic advantages and substantially improves the cleaning action on the Si surface. The oxidizing action of ozone on the Si surface is also improved by the process according to the present invention.
The semiconductor wafers used in the process according to the invention, which have been treated with a medium containing HF and are free of aqueous HF, can be obtained as a result of either carrying out the treatment with the medium containing HF
a) by using HF gas or
b) after the treatment in the aqueous HF bath has been carried out, separating the semiconductor wafer from the latter in such a way that there is no longer any aqueous HF on the surface of the semiconductor wafer.
In the process variant a) the semiconductor wafers are exposed to an HF gas stream in a sealed device, and the residual HF gas is pumped out at the end of the treatment stage. The semiconductor wafers obtained in this way can then be processed using ozone gas in a second step. The residual ozone gas is pumped out after the ozone-gas treatment stage.
In the process according to the invention, the semiconductor wafer treated with HF can be separated from the aqueous HF bath according to the process variant b) by
b1) extracting the aqueous HF solution from the treatment bath or
b2) extracting the treated semiconductor wafers from the aqueous HF bath.
In the process according to the present invention, in the variant b1) the aqueous HF solution is preferably discharged from the process bath into a temporary container at a rate which lowers the level of the liquid by preferably from 0.01 to 15 mm per second and more particularly from 0.01 to 0.5 mm per second. In this case, the HF solution is preferably discharged a valve that has a controllable cross section. After the HF solution has been fully drained from the bath, the semiconductor wafers that are free of HF solution are immersed in the next medium containing ozone. The HF solution is cleaned in the temporary container, preferably by using 0.05 xcexcm recycling filtration, and fed back into the process bath. The filtered HF solution is again ready to clean semiconductor wafers.
In the process according to the present invention, in the variant b2) the treated semiconductor wafers are drawn at a speed of preferably from 0.01 to 15 mm per second and more particularly from 0.01 to 0.5 mm per second through the surface of the aqueous HF solution, advantageously by using an automated handling device. The semiconductor wafers obtained in this way, which are free of HF solution, are subsequently immersed in the next medium containing ozone, and uniformly rendered hydrophilic.
The process according to the present invention is carried out at a temperature of preferably from 10 to 65xc2x0 C., particularly preferably from 20 to 30xc2x0 C., and at a pressure of preferably from 900 to 1100 hPa.
The treatment sequences according to the present invention mayxe2x80x94if desiredxe2x80x94be preceded or followed by other standard operations for the chemical treatment of semiconductor wafers, for example treatment to dry the semiconductor wafers after the ozone treatment has been carried out.
The present invention provides a process with which semiconductor wafers can be conditioned particularly effectively for the defect-free growth of thermal oxides.
The process according to the present invention has the advantage that the native oxide grows very uniformly over the entire Si surface during the ozone hydrophilization. The oxide advantageously contains no defect sites in the native oxide, which cause nonuniform thermal oxidation in the nm range. According to the requirement of the subsequent processing in the IC industry, very thin or thick oxide layers are applied to the semiconductor wafer. The thermally produced oxide layers grow uniformly and without defect regions.
The process according to the present invention also has the advantage that the Si surface of the semiconductor wafer is free of regions with different microroughness (haze) due to residual aqueous HF solution in combination with aqueous ozone solution.